Heat Resistant High Chemical Versatility Alluminum Alloy to Produce Aerosol Cans

ABSTRACT

A heat resistant high chemical versatility aluminum alloy to produce aerosol cans contains alloyings in the following weight percentages: 0≤Si≤0.60%, 0≤Fe≤0.80%, 0≤Mn≤0.80%, 0≤Ti≤0.10%, 0.05≤Zr≤0.30%, 0≤Cu≤0.10%, 0≤Mg≤0.10%, 0≤Zn≤0.30%, 0≤V≤0.03%, with the remainder being Al.

BACKGROUND

Nowadays, aerosol cans are produced from different 1000 and 3000 series aluminum alloys as per the European Norm EN 573-3. The most common alloys are EN AW 1070A, with a total Aluminum (Al) content of 99.7%, EN AW 3102 with an approximate 0.3% content of Manganese (Mn), and EN AW 3207 with an approximate 0.6% content of Mn. According to this standard, alloys have specifically the following alloying concentrations in percentage weight:

EN AW 1070: Si≤0.20; Fe≤0.25; Cu≤0.03; Mn≤0.03; Mg≤0.03; Zn≤0.07; Ti≤0.03; V≤0.05; Al=99.7 minimum.

EN AW 3102: Si≤0.40; Fe≤0.70; Cu≤0.10; Mn=0.05-0.40; Zn≤0.30; Ti≤0.10; Al=remainder.

EN AW 3207: Si≤0.30; Fe≤0.45; Cu≤0.10; Mn 0.40-0.80; Mg≤0.10; Zn≤0.10; Al=remainder.

Aluminum ingots or discs made from the aforementioned alloys are used for the container production process. The production process can be divided in 3 great manufacturing stages.

1^(st) Stage: Continuous Process to Manufacture Spools

-   -   Filling the cast furnace with liquid electrolytic aluminum.     -   Filling the cast furnace with aluminum cuttings from the cut and         stamp process.     -   Furnace alloy with the different components according to the         alloy to be cast.     -   Continuous cast of an aluminum sheet by means of a casting         wheel.     -   Aluminum sheet hot rolling.     -   Aluminum sheet cold rolling.     -   Spooling of the sheet.

2^(nd) Stage: Process to Manufacture Ingots

-   -   Aluminum sheet unspooling.     -   Cutting and shaping of the ingots by means of a press.     -   Thermal treatment of the ingots annealing.     -   Cooling of the ingots.     -   Superficial treatment (drumming or blasting).     -   Fractioning and final packaging.

3^(rd) Stage: Aerosol Container Manufacturing Process

-   -   Lubricating the ingots.     -   Extrusion by impact.     -   Cutting the edge of the container.     -   Brushing the container.     -   Washing and degreasing the container.     -   Applying inner varnish and curing in polymerization furnace.     -   Applying base enamel and curing in oven.     -   Applying the decoration dies and curing in oven.     -   Applying protective coat and curing in oven.     -   Shaping the neck and profile of the container.

Given the mechanic features of aluminum for high mechanical distress and hardening by hammering, these make it ideal to manufacture aerosol containers using extrusion by impact. The 3000 series alloys, such as those in EN AW3102 and EN AW3207, offer better mechanical features compared to EN AW1070A, therefore rigidity and resistance to aerosol container internal pressure are improved. However, the mechanical conditions of the three alloys mentioned change substantially when the container undergoes the internal varnish curing process in the polymerization furnace. In this process, the material is subjected to temperatures of between 210 and 250° C. for 10 minutes. At these temperatures, aluminum suffers a partial annealing thermal treatment. As a result, there is a loss of hardness and mechanical resistance necessary to withstand the strains of the following processes of neck and profile shaping essential to obtain high productivity. Moreover, the damage to mechanical resistance generates a decrease in the aerosol filling pressures which involves a loss in the filling capacity and the quality of the performance of the final product. For the latter element, a change in design could be proposed, e.g., through increasing the thickness of the container and, consequently, its resistance; however, this entails an increase in costs and a loss of competitiveness since it is necessary to use more raw material and energy in the different steps of the process detailed above.

In order to bypass this issue, different attempts have been tried to improve the chemical compositions of the standardized alloys, working hard on controlling the chemical composition and adding new elements to the alloy, mainly zirconium (Zr), which is capable of increasing the recrystallization temperature for aluminum alloys and thus decreasing the loss of hardness and mechanical resistance during the heating process for the aerosol can interior varnish curing.

Some attempts to use the modification on the chemical compositions of the alloys were disclosed in European patents No. EP 2 881 477 B1, EP 3 009 524 A1, and EP 3 031 941 A1, wherein the three modifications to standard alloys by adding zirconium and guaranteeing an improvement in the heat resistance for the manufacture of aerosol cans are defined. On the other hand, the background disclosed in European patent No. EP 3 075 875 A1 define an aluminum alloy to manufacture aerosol cans by extrusion by impact and the procedure to manufacture them, where zirconium is used again as main variant, as well as other modifications to the chemical composition ranges for the other elements. The aluminum alloy proposed in said patent asserts to provide constant mechanical properties before and after polymerization, so the issue of the decrease in mechanical properties after the internal color drying process (after polymerization) would be solved. However, the background considered above has a limitation due to the need of a strict control of the chemical composition ranges for the different elements in the alloy, even for the zirconium contents, as well as other elements deemed impurities, e.g., to achieve a strict control of the alloy limits, European patent No. EP 3 075 875 A1 proposes the preparation from high purity aluminum (electrolytic aluminum) and scrap or return stamp which must be melted in a first stage where the slag is removed; then the liquid aluminum is poured in another oven where the alloy and the chemical composition adjustment are done with takes place using master alloys. Said limitation creates not only more strict controls for the process but also a greater difficulty to use scrap as return for the preparation of new alloys.

Nevertheless, an embodiment of this invention proposes the manufacture of an alloy using a unique melting process in which the liquid bath is prepared with high purity aluminum (electrolytic aluminum) and scrap or return in about 40% weight of the oven load. Moreover, both the preparation and the control of the alloy elements are done in the same melting furnace with the addition of master alloys and then the liquid metal is in condition to be cast. Thus narrower margins are obtained in the alloy chemical composition. Later, using a combination of cast conditions, plastic shaping and thermal treatment, the features needed to comply with the recrystallization temperature properties are achieved with a low hardness loss and mechanical resistance in the container.

BRIEF DESCRIPTION OF THE INVENTION

Regarding the mentioned background, as well as for traditional standard alloys, this invention proposes an improvement as far as the versatility in the chemical composition ranges used in the manufacture of the proposed alloy, as well as the addition of new alloy elements which allow improvements in its properties, preventing losses in mechanical resistance and showing improvement in the stability of said mechanical resistance after being subjected to curing temperatures in the oven. The possibility to handle a greater amplitude range in the alloy chemical composition allows to use a greater proportion of scrap (return) during the liquid bath preparation than the one used in the prior art processes, thus promoting a process with raw material reutilization, decrease in energy consumption, decrease in production costs and decrease in environmental impact for the process.

Table 1 shows the different alloys proposed in the aforementioned background, together with an alloy chemical composition according to an embodiment of this invention, which was called ZIRARG.

TABLE 1 Chemical composition of the alloys proposed by background and the invention. Concentration in alloying percentages by weight (% Wt/Wt) Si Fe Mn Ti Zr Cu Alloys Min. Max. Min. Max. Min. Max. Min. Max. Min. Max. Min. Max. EP 2 881 477 0.00 0.25 0.00 0.40 0.00 0.05 0.00 0.05 0.10 0.15 0.00 0.05 B1 EP 3 009 524 0.00 0.40 0.00 0.70 0.05 0.40 0.00 0.10 0.05 0.20 0.00 0.10 A1 EP 3 031 941 0.00 0.30 0.00 0.45 0.40 0.80 0.00 0.05 0.05 0.20 0.00 0.10 A1 EP 3 075 875 0.05 0.20 0.10 0.55 0.01 0.60 0.00 0.03 0.05 0.20 0.00 0.01 A1 ZIRARG 0.00 0.60 0.00 0.80 0.00 0.80 0.00 0.10 0.05 0.30 0.00 0.10 Total alloying considering the maximum Concentration in alloying percentages by weight (% Wt/Wt) allowed Mg Zn V concentration Alloys Min. Max. Min. Max. Min. Max. Al limit (% Wt/Wt) EP 2 881 477 0.00 0.05 0.00 0.07 — — remainder 1.07 B1 EP 3 009 524 0.00 0.01 0.00 0.30 — — remainder 2.21 A1 EP 3 031 941 0.00 0.10 0.00 0.10 — — remainder 2.10 A1 EP 3 075 875 0.00 0.01 0.00 0.02 — — remainder 1.62 A1 ZIRARG 0.00 0.10 0.00 0.30 0.00 0.03 remainder 3.13

The purpose of this invention shall be to solve the inconveniences detailed in the prior art, improving the conditions of the traditional alloys chemical compositions, with versatility and a guarantee of improved mechanical resistance for the final conditions needed to comply with the most demanding product standards for said alloy: aerosol containers. For this purpose, in an embodiment of this invention there is an alloy called ZIRARG, the preparation of which is done by a liquid state casting process, combining raw material in electrolytic liquid aluminum form (primary aluminum) and scrap or return from the ingots manufacturing process (secondary aluminum) which is finally going to deliver a material with the chemical composition detailed in Table 1.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a graph comparing the traction resistance assays at different alloy temperatures corresponding to an embodiment of this invention regarding alloys known in the prior art.

FIG. 2 shows the results of the load test needed to produce a deformation or breakage of the container rim for M3 alloy (EN AW 3102) and ZIRARG alloy.

FIG. 3 details the results of the load test that generates the deformation or breakage of the container shoulder for M3 alloy (EN AW 3102) and ZIRARG alloy.

FIG. 4 shows the internal pressure necessary to generate deformation and crumbling of the container manufactured with M3 alloy (EN AW 3102) and ZIRARG alloy.

FIG. 5 schematizes the complete process for the continuous manufacture of spools of ZIRARG alloy.

DETAILED DESCRIPTION OF THE INVENTION

The ZIRARG alloy, according to one embodiment of this invention, is prepared from liquid aluminum resulting from the primary electrolytic process (primary aluminum) which represents between 50% and 60% of the melting furnace, preferably 60%. Then a solid scrap (return) load from the ingots manufacture representing between 40% and 50% of the melting furnace load is placed in the furnace, preferably 40%. Once the melting and homogenization are done at approximately 770° C., the creation of the ZIRARG alloy will proceed by adding the alloyings using master alloys containing the different chemical elements of interest and the final concentrations of all the alloy elements (Si, Fe, Mn, Ti, Zr, Cu, Mg, Zn, V) will be obtained. Thus the composition will be adjusted within the ranges established for it and the cast will be produced with the liquid bath treatment through a grain refining, degassing and filtering of the liquid metal in the cast channel to be finally continuously cast in the shape of metal sheets. The subsequent combination of hot plastic shaping thermal-mechanical processes, cold plastic shaping, calibration of the desired final sheet thickness and annealing thermal treatments will give the ingots the mechanical properties set necessary to manufacture the aerosol containers which will allow a high recrystallization temperature without damaging mechanical properties.

According to one embodiment of this invention, the liquid aluminum is prepared in at least two tilting melting furnaces to allow a continuous flow of the alloy to feed a continuous cast. Melting furnaces are used to cast, deslag, alloy and run aluminum. When one of the furnaces is empty, the bottom and sides are cleaned to remove the slag, it is loaded with a 60% load of primary liquid aluminum (electrolytic aluminum) and the remaining 40% with solid aluminum. The solid aluminum comes from the scrap from the productive process of ingot manufacture by cutting and pressing. Then the furnace temperature is stabilized and all the material is cast, a sample of aluminum is taken to analyze the chemical composition and assess which alloyings and what amounts must be incorporated to obtain the desired alloy.

-   -   The Fe, Si, Mn and Zr alloyings are selected and weighed, they         are incorporated into the furnace and the mixture is done in the         furnace using great pallets moved by an auto-lifter. The mixture         is left to rest for approximately 30 minutes. The pallet is pass         over the surface to remove remaining slag from the furnace.     -   A sample is taken to analyze again the chemical composition and         assess whether the alloy prepared is within the parameters.         Generally, at this time the furnace is left according to         specification, but it may need a second alloy stage, so the         alloyings are placed, the material is mixed and the analysis is         done again.     -   In all the process, the furnace temperature is between 740° C.         and 790° C.

The aluminum leaves the furnace through a refractory material channel at 750-760° C. The channels have thermal caps to maintain the temperature of the liquid aluminum. Along the first stretch of 6 m in length the aluminum, titanium and boron wire rod is incorporated (Al—Ti 5%-B 1%). This addition is aimed at obtaining the grain refining of the alloy. For the next two meters of cast channel, the liquid aluminum enters a degassing device where Ar 99,998 pure is injected using a graphite rotor. This stage is aimed at decreasing the impurities and gaseous hydrogen contents occluded in in aluminum.

Following the degassing there is a ceramic filter with a mesh size of approximately 50 μm, where the liquid aluminum is cleaned from solid undissolved impurities. At the end of the cast channel there is the cast wheel, which consists of a Properzi-type wheel, made from Cu and a groove will give the geometry to the cast metal sheet. During the cast, the aluminum enters the wheel at approximately 700° C. The wheel is cooled with water to approximately 20° C., so as to solidify the aluminum constantly and homogeneously. Exiting the wheel there is a continuous aluminum sheet at 520° C. The cast wheel is regularly lubricated using a suspension of water and 4% graphite.

In one embodiment of this invention, the sheet exiting the cast wheel enters a hot mill. The sheet is refrigerated and lubricated using an emulsion of water and 6% oil at 55° C. The mill reduces the thickness in one step, e.g., from 22 mm to 8 mm. Once the sheet is reduced, it is refrigerated using a water tank. Exiting the water tank, the sheet is at approximately 60° C. and then air blowers are used to eliminate water drops from the sheet surface so it enters the cold mill completely dry. The cold mill is lubricated with oil and high compression additives. The exiting thickness is variable according to the product and ranges from 4 mm to 7 mm final thickness. Thickness control is done automatically by 2 X-rays heads which constantly measure the sheet as it enters and exits the mill.

Once the cold lamination is finished, the sheet is spooled in rolls and sent to cool naturally or helped with a fan to lower the temperature to at least 30° C. to continue the press process and ingot manufacture.

In one embodiment of this invention, the cooled spools are placed in a despooling chuck on a press to do the ingot cut. The despooling is used to stretch the sheet over a roller bed to dose the sheet to the cutting press.

In an embodiment of this invention, the ingot cutting and shaping process consists in placing the metal sheet in a cutting die. By a downward vertical movement of the superior die the metal sheet is cut and shaped. The final product is an aluminum ingot or disc.

In an embodiment of this invention, the ingots obtained in the press are thermally treated using an annealing process to recrystallize the crystalline structure and achieve the mechanical features that will allow the extrusion process to create the container. The annealing condition is verified ensuring the process parameters and controlling the surface hardness in an ingot sample. Depending on the alloy, the hardness of an ingot with thermal treatment is between 17 and 28 HB, and of an ingot without thermal treatment is between 30 and 58 HB.

The ingots are taken to a temperature of 500° C.+/−10° C. and they are kept at this temperature for 70 minutes. Once the treatment time is over, the cycle is cut and the load is placed at room temperature, where it cools naturally or forced with fans and enters a second platform for a second treatment. A semi-continuous process can also be used to obtain similar results.

In an embodiment of this invention, a superficial drumming or shot peening treatment is done to give the ingot roughness to its entire surface so in the extrusion process the lubricant can adhere, since an ingot without superficial treatment would have a very smooth and uniform surface and the lubricant would not adhere. The roughness measure obtained is approximately: Ra (arithmetic mean roughness)>3 μm and Rpc>30 1/mm (roughness density).

The aerosol can manufacture process according to an embodiment of this invention is composed by different stages. First a paste lubricant must be applied to the ingot using a drumming process. The body of the aerosol can is formed from an ingot subjected to extrusion by impact using a press. In an embodiment of this invention, the press applies approximately 200 hits per minute.

After the extrusion, in an embodiment of this invention the internal coating of the container is done applying a lacquer on the aerosol can surface and color polymerization is done at approximately 250° C. for between 10 and 15 minutes. Then the external coloring process continues, where a protective base over the entire external layer of the container which is then subjected to a drying cycle at 150° C. Then the lithography process continues, where the decoration or design for the container is applied in all the colors and the drying process is done again at 150° C. There follows the varnishing of the external layer, which is dried at 190° C. In the last stage the neck and shoulder of the container are shaped.

Assays

Additionally there were mechanical assays conducted for an alloy with chemical composition according to the preferred embodiment of this invention (ZIRARG): Si: 0.08%; Fe: 0.25%; Mn: 0.32%; Ti: 0.09%; Zr: 0.15%; Cu: 0.001%; Mg<0.001%; Zn: 0.004%; V: 0.001%; Al: remainder. The results obtained with the containers manufactured using the different traditional alloys compared to the ZIRARG alloys, according to this invention, show that after being subjected to different temperatures in the enameling and curing process in the furnace, the mechanical resistance drops as anticipated for traditional alloys, however, for the ZIRARG alloy of this invention, the resistance to traction is practically not modified during the thermal treatment produced in the alloy (FIG. 1). Also, axial load assays were conducted on the rim and shoulder, such as pressure assays for the different containers manufactured with standard traditional alloys and the ZIRARG alloy of this invention. FIGS. 2 and 3 detail the results obtained, where it can be seen that there is an increase in compression resistance for the containers made with the ZIRARG alloy. Moreover, FIG. 4 shows the results of the internal pressure tests conducted in both instances of deformation and crumbling on aerosols manufactured with the alloy of this invention and aerosols manufactured with the traditionally used alloy M3 (EN AW 3102) where an increase in resistance to internal pressure can be seen in the cans manufactured with the proposed ZIRGARG alloy.

FIG. 1 shows the ratio between resistance to traction for traditional alloys and ZIRARG alloy for the different stages of the aerosol container manufacturing process, where samples were taken after the container extrusion, during the curing process at 210° C. for about 10 minutes and with a curing process at 250° C. for about 10 minutes. The results show that for the ZIRARG alloy there is a greater resistance to traction for the curing conditions with greater temperature requirements (250° C. for about 10 minutes).

FIG. 2 shows the results of the load test needed to produce a deformation or breakage of the container rim for M3 alloy and ZIRARG alloy. It is observed that for the ZIRARG alloy it is necessary a greater load to produce breakage or deformation of the rim. This represents a benefit in the final mechanical resistance of the container, obtaining greater filling internal pressures and the possibility to decrease the thickness of the container in future developments.

FIG. 3 shows the results of the load test that generates the deformation or breakage of the container shoulder for M3 alloy and ZIRARG alloy. It is observed that for the ZIRARG alloy it is necessary a greater load to produce breakage or deformation in that area of the container.

FIG. 4 shows the internal pressure necessary to generate deformation and crumbling of the container manufactured with M3 alloy and ZIRARG alloy. A greater internal pressure is observed for the tests done with the ZIRARG alloy compared to those done with the traditional M3 alloy.

FIG. 5 schematizes the complete process for the continuous manufacture of spools of ZIRARG alloy. The process is detailed from the melting in the furnaces, to the cast and purification process, to the hot and cold rolling to reduce the thickness needed to obtain the spool of ZIRARG material in condition to be sent to manufacture the ingots.

Reference document: Aluminum and Aluminum Alloys (Asm Specialty Handbook) ISBN: 087170496X. 

1-2. (canceled)
 3. A heat resistant high chemical versatility aluminum alloy to produce aerosol cans containing the following alloyings in weight percent: 0≤Si≤0.60%; 0≤Fe≤0.80%; 0≤Mn≤0.80%; 0≤Ti≤0.10%; 0.05≤Zr≤0.30%; 0≤Cu≤0.10%; 0≤Mg≤0.10%; 0≤Zn≤0.30%; 0≤V≤0.03%; and Al as the remainder.
 4. The aluminum alloy according to claim 3, wherein the alloyings in weight percent are: Si: 0.08%; Fe: 0.25%; Mn: 0.32%; Ti: 0.09%; Zr: 0.15%; Cu: 0.001%; Mg: 0.001%; Zn: 0.004%; V: 0.001%; and Al as the remainder. 